Hello @Naomi75,
The host has already satisified Airbnb's scoring system requirements by responding to you with a pre-approval.
Had they just messaged you in response to your inquiry then their respponse time stat would be reduced.
But since they've pre-approved you within 24 hours their response time is all OK.
They can remove the pre-approval or just let it expire with no affect on their response time.
As a prompt for them to remove it you can tell them that this article What is a pre-approval? says:
After 24 hours, the guest can still request to book your listing with the price offered during the pre-approval, unless you remove the pre-approval.
If they don't remove it and later increase their prices, their older, lower prices, are still valid for you.
Steve.